Hot catalysts make for a clean cold start

THANKS largely to their catalytic converters, today’s cars create far fewer harmful emissions than older cars – except for the first few minutes of every trip. Now an American company has developed a device to overcome the “cold-start” problem, caused by the time it takes for catalysts to reach their working temperature. Ergenics of Ringwood, New Jersey, has developed a metal hydride device that heats the catalyst in just a few seconds. It then uses heat from the engine to recharge itself.

David DaCosta, president of the company, says&colon; “It takes the catalytic converters on today’s cars between one and two minutes to reach ‘light-off temperature’, which is about 350 °C. Before they heat up, the exhaust and unburned fuel go right through.”

The heating device stores hydrogen in solid form, absorbed in a metal hydride. When the driver turns the ignition key, a valve in the heater unit opens to allows about 2 grams of hydrogen gas to flow from the metal hydride into a proprietary metal alloy to produce almost instant heat. “The exothermic reaction in the heater bed raises its temperature to 400 °C in about five seconds,” says DaCosta. “This heats the exhaust, which in turn heats the catalytic converter. The converter is up and functioning in less than 10 seconds.”

After the engine has run for a few minutes, heat from its exhaust warms the heater bed to over 450 °C, when the hydrogen is driven off the alloy, and back into the metal hydride. According to DaCosta, the entire cycle can be completed in a five-minute trip. During shorter trips, the heater will be only partially regenerated.

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The main rival technology to tackle cold starts is electrical heating. W R. Grace has created prototype electric heaters that can heat cold exhaust systems in a few seconds. They weigh less than the Ergenics heater – about 1 kilogram compared to 2.5 kilograms – but they have the drawback of draining the car’s battery.

Neither approach has yet been adopted by the major car companies. DaCosta says that car makers have so far concentrated on reducing emissions by improving catalysts and making cleaner burning engines, rather than going to the expense of adding heaters. “But if emissions requirements become stricter, I believe we will see cold-start heaters on some vehicles, especially those with V-8 engines, whose converters are slower to heat up and function.”